Fluid operated actuators convert a fluid pressure to a work piece using an actuator that typically consists of a piston in a cylinder. Although there are various suitable fluids that may be used, the fluid applied to the actuator generally comprises pneumatic or hydraulic fluid, for example. Pneumatic operated actuators are generally used where the compressibility of air is desired or to obtain much higher flow rates and thus faster response times while hydraulic operated actuators are generally employed when high actuating forces are required. Both fluids have advantages and in some situations, either pneumatic or hydraulic fluid may be used.
Although fluid operated cylinders are generally known in the art, one particular type of fluid operated cylinder comprises an impact cylinder. Impact cylinders, also known as drop hammers, are generally known in the art and used for a variety of applications. Impact cylinders may be powered using a variety of different fluids or other actuators; however, it is particularly common to use fluid pressure, such as pneumatic or hydraulic fluid, to pressurize the impact cylinder. Generally, fluid pressure is introduced into a first fluid chamber resulting in the movement of a piston. Towards the end the piston's stroke, it collides with a secondary piston or other striking member. The striking member then rapidly extends from the cylinder body, thereby impacting some work piece. Another variation is to omit the striking member and have a piston rod, coupled to the piston, strike the work piece directly.
Impact cylinders can be used for a number of applications. For example, in waste combustion plants, deposits can form on the exhaust pipes resulting in the pipes becoming clogged. An impact cylinder can be coupled to the exhaust pipes and when actuated, the striking pin impacts the exterior of the pipe to break loose and de-cake the inside of the pipe. With a single strike of the striking pin, the pipe can continue to vibrate to break loose more deposits.
Although impact cylinders have received great success, one potential problem encountered when using impact cylinders is rebound striking by the striking pin. Rebound striking can occur when the striking pin impacts either the work piece or the piston multiple times during the course of a single piston stroke. In use, the rear cylinder chamber of the main piston is rapidly pressurized in order to actuate the piston with sufficient force and speed. However, after actuation, this pressure remains in the rear cylinder and also acts on the striking pin, preventing the striking pin from fully retracting. If this pressure is not exhausted, the striking pin can impact the work piece multiple times, which may not be desirable. Prior art attempts to provide exhaust valves to vent the rear cylinder chamber typically takes a significant amount of time and requires complex control systems and large ventilators resulting in increased expense.
Therefore, there exists a need for an impact cylinder that can rapidly compensate for the force acting on the main piston after the impact cylinder has been actuated. The present invention overcomes this and other problems and an advance in the art is achieved.